Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.52   9.559%   $235.026   $235.03   $235.05   $235.00  
  Purchase #2 $104.95   11.514%   $117.0339   $117.03   $117.05   $117.00  
  Purchase #3 $238.98   4.862%   $250.5992   $250.60   $250.60   $250.60  
  Purchase #4 $154.25   12.190%   $173.0531   $173.05   $173.05   $173.10  
  Purchase #5 $34.72   12.502%   $39.0607   $39.06   $39.05   $39.10  
  Purchase #6 $248.64   3.758%   $257.9839   $257.98   $258.00   $258.00  
  Purchase #7 $250.77   10.410%   $276.8752   $276.88   $276.90   $276.90  
  7 purchase totals = $1,246.83       $1,349.6320   $1,349.63   $1,349.70   $1,349.70